松辽盆地北部白垩系泉头组扶余致密砂岩储层发育微纳米级孔隙、微裂缝,且孔缝结构复杂,导致成藏期致密油气在不同类型储集空间中的充注顺序不清,增加了致密油气的勘探开发难度.本文针对致密砂岩储层中不同充注压力条件下致密油的充注特征开展定量研究,结合大视域拼接扫描电镜与矿物面扫技术,提出了一种基于孔隙-微裂缝组合的致密油充注规律微观评价方法.研究表明,区内泉头组扶余致密砂岩储层主要发育 3种孔缝组合类型:粒间孔-黏土矿物收缩缝、粒间孔-脆性矿物粒间缝及黏土矿物晶间孔-收缩缝组合.通过将具有高温流变性质的伍德合金在不同压力下注入岩心,可以观察到合金在不同孔缝组合类型中的注入随注入压力提升而表现出有序性,粒间孔、缝的充注优先级明显高于黏土矿物相关孔缝,伍德合金的注入效率呈明显的先快速增大后缓慢增大最终趋于稳定的抛物线形态.依据伍德合金与原油的性质特征,将注入压力进行了等效转化,还原了地层条件下致密油的微观充注过程,据此建立了致密储层孔缝序列充注模式.在高源储压差条件下,致密油能够充注至纳米级的黏土矿物晶间孔-收缩缝中,随源储压差降低,致密油逐渐难以充注至纳米级孔缝中.当源储压差降至最低时,致密油仅能通过渗吸的方式通过宽大的孔间连通喉道进入微米级粒间孔及连通性较好的铸模孔中.本研究将流体注入与可视化技术相结合进行致密储层的储集空间多尺度评价,为致密储层微观甜点评价及高效开发提供参考.

The development of micro-nano-scale pores and microfractures in the Fuyu tight sandstone reservoirs of the Cretaceous Quantou Formation in the northern part of the Songliao Basin,as well as the complex structure of the pores and fractures,leads to the unclear sequence of tight oil and gas filling in different types of reservoir spaces during the formation period,which increases the difficulty of exploration and development of tight oil and gas.In this paper,a quantitative study is conducted on the filling characteristics of tight oil under different filling pressures in tight sandstone reservoirs,and a microscopic evaluation method of tight oil filling patterns based on pore-microfracture combinations is proposed by combining large field-of-view splicing swept electron microscopy and mineral surface scanning technology.The study shows that the Fuyu tight sandstone reservoirs of the Quantou Formation in the area can be classified into three main types of pore-fracture combinations:intergranular pore-clay mineral shrink fractures,intergranular pore-brittle mineral intergranular fractures and clay mineral intergranular pore-shrink fractures combinations.By injecting Wood's alloy with high-temperature rheological properties into the core at different pressures,it can be observed that the injection of the Wood's alloy in the different pore-fracture combinations shows orderliness with the increase of injection pressure,and the filling priority of the intergranular pores and fractures is obviously higher than that of the clay mineral-related pores and fractures,and the injection efficiency of Wood's alloy shows an obvious parabolic pattern of rapid increase first,followed by a slow increase that tends to be stable eventually.Based on the properties of Wood's alloy and crude oil,the injection pressure was equivalently transformed to simulate the microscopic filling process of tight oil under stratigraphic conditions,and accordingly the pore and fracture sequence filling model of a tight reservoir was established.Under the condition of high source storage pressure difference,the tight oil can be filled into the nanoscale intergranular pore-shrink fractures of clay minerals,and with the decrease of source storage pressure difference,the tight oil is gradually difficult to be filled into the nanoscale pore and fractures.When the source storage pressure difference is reduced to the lowest,the tight oil can only enter the micron-sized intergranular pores and the well-connected mould pores through the wide intergranular connecting throat by means of osmosis.This study combines the fluid injection and visualization techniques for the multi-scale evaluation of reservoir space in tight reservoirs,which is of great significance for the evaluation of microscopic sweet spots and efficient development of tight reservoirs.